1. Field of the Invention
The present invention relates to a permanent-magnet electric rotating machine, and particularly relates to a permanent-magnet electric rotating machine with a concentrated winding stator suitable to windings with thick wire.
2. Description of the Related Art
A large current of a low voltage is fed to an electric rotating machine using a battery or the like as power source. Therefore, thick wire windings are used as a stator windings wound on stator magnetic poles of such an electric rotating machine in order to reduce the resistance value of the windings.
A stator used in a conventional electric rotating machine of such a type will be described with reference to FIG. 19.
FIG. 19 is a cross-sectional view of a stator 84 of a conventional electric rotating machine, viewed in its axial direction. Twelve stator magnetic poles 85a1 to 85a12 are formed at circumferentially equal intervals so as to radially extend from a yoke 86 toward the center of the stator. In addition, the stator magnetic poles 85a1 to 85a12 have circumferentially widened top end portions 85b1 to 85b12 respectively. The reference numeral W0 designates a slit width between adjacent stator magnetic poles, for example, 85a1 and 85a2, and so on. A bottom portion 87a of each slot 87 formed between adjacent stator magnetic poles is shaped to be an arc.
Generally, a permanent-magnet electric rotating machine has stator magnetic poles, and, conventionally, in such a permanent-magnet electric rotating machine, stator windings are concentratedly mounted on the magnetic poles. In such a conventional permanent-magnet electric rotating machine, it is general that the ratio of the number M of the magnetic poles of the stator to the number P of the magnetic poles of the permanent magnet is set to 3:2, that is M:P=3:2. Further, a motor winding and a generator winding are wound in one and the same slot.
In such a conventional electric rotating machine with a concentrated winding stator, however, there have been some problems as follows.
(1) In the stator of such a conventional electric rotating machine, the top end portions of the stator magnetic poles are circumferentially widen as shown in FIG. 19. Accordingly, the slit width between adjacent stator magnetic poles is narrow. When thick-wire windings are to be wound on the respective stator magnetic poles by use of a nozzle of a winding machine, the width of the nozzle is limited because the slit width passed by the nozzle is narrow, so that it has been impossible to mount such thick-wire windings.
(2) In addition, if a windings in which thick wire is wound on a bobbin in advance is to be used, the slit width is too narrow to mount onto a stator magnetic pole from the radial center side of the stator.
(3) Further, because the bottom portion of each slot is shaped to be an arc, the slot area is small, and the total number of turns of the windings is limited.
(4) Moreover, because the ratio of the number M of the magnetic poles of the stator to the number P of the magnetic poles of the permanent magnet is set to M:P=3:2, cogging torque is large, and the winding factor expressing the effective utilization ratio of the winding takes a small value of 0.866. Therefore, in the electric rotating machine, the motor torque is small, and the voltage generated by a generator is low.
(5) Further, because the ratio of the number M of the magnetic poles of the stator to the number P of the magnetic poles of the permanent magnet is set to M:P=3:2, it is impossible to dispose motor winding sets and generator winding sets on the stator magnetic poles independently of each other. Accordingly, insulation is used in common to both the winding sets, so that the safety is inferior.
It is an object of the present invention to provide a permanent-magnet electric rotating machine with a concentrated winding stator in which the foregoing problems in the conventional electric rotating machine can be solved.
In order to achieve the above object, according to an aspect of the present invention, provided is a permanent-magnet electric rotating machine with a concentrated winding stator, including a stator having a plurality of stator magnetic poles formed so as to extend radially from an annular yoke portion of a stator iron core, and windings mounted on the stator magnetic poles; and a rotor having a permanent magnet with a plurality of magnetic poles and rotatably held so as to face the stator through an air gap; wherein each of the stator magnetic poles has a straight shape having a width which is made constant over a whole length, small grooves are formed in each of the stator magnetic poles in symmetrical positions on opposite sides and near a top end portion of the stator magnetic pole, a bottom portion of each slot portion defined by adjacent ones of the stator magnetic poles and the yoke is formed triangularly, each of the stator winding is constituted so that a winding having a predetermined number of turns and winding being formed so as to be fittable to each of the stator magnetic poles is mounted on the stator magnetic pole through an insulator, and wedges are fitted to the small grooves formed in the stator magnetic poles.
According to this configuration, each of the stator magnetic poles is formed so as to have a straight shape in which the width of the magnetic pole is made constant and the slot has a bottom portion which is formed to be triangular, as mentioned above. Accordingly, the slit width between stator magnetic poles adjacent to each other is widened. Therefore, stator windings which are bobbin-wound with thick wires in advance can be mounted on the stator magnetic poles from the radial center side of the stator iron core.
Further, the slot area is increased so that it is possible to increase the total number of turns of the stator windings.
In the above permanent-magnet electric rotating machine with a concentrated winding stator, preferably, each of the stator windings includes motor windings and generator windings, the motor windings being mounted on every two of, that is, a half of the stator magnetic poles, while the generator windings are mounted in the same manner in the rest half of the stator magnetic poles.
With such a configuration, insulations for the motor windings and the generator windings are separated perfectly. Accordingly, it is possible to obtain an electric rotating machine in which the safety is improved. In addition, it is possible to reduce the number of terminals of the windings to be processed.
In the above permanent-magnet electric rotating machine with a concentrated winding stator, preferably, the number of turns of the motor windings is made different from that of the generator windings.
With such a configuration, it is possible to increase the generator output voltage taking the voltage drop due to a load in the generator output into consideration in advance.
In the above permanent-magnet electric rotating machine with a concentrated winding stator, preferably, the relationship between the number M of the stator magnetic poles and the number P of the magnetic poles of the permanent magnet is set to satisfy conditions of (2/3) less than (P/M) less than (4/3) and Pxe2x89xa0M.
With such a combination of the numbers M and P in the conditions mentioned above, it is possible to obtain the above-mentioned winding factor expressing the effective utilization ratio of the stator windings the value of which is equal to or larger than that in the conventional case.
In the above permanent-magnet electric rotating machine with a concentrated winding stator, preferably, the relationship between the number M of the stator magnetic poles and the number P of the magnetic poles of the permanent magnet is set to satisfy a condition of M:P=6n:(6nxc2x12) (n being an integer not smaller than 2).
With such a ratio of the number M to the number P, the winding factor takes a large value of 0.933 in the case of n=2, 0.970 in the case of n=3 and 0.983 in the case of n=4. Accordingly, the electric rotating machine having a large motor torque, a high generator voltage, and a small cogging torque can be obtained.